BUTTERFLY PSYCHOLOGY. 147 



external stimulants of sight, smell, or touch 

 set up the appropriate actions in the man- 

 dibles, just as contact of the lips with an 

 external body sets up sucking in the infant. 

 All these movements depend upon what we 

 call instinct that is to say, organic habits 

 registered in the nervous system of the race. 

 They have arisen by natural selection alone, 

 because those insects which duly performed 

 them survived, and those which did not duly 

 perform them died out. After a considerable 

 span of life spent in feeding and walking about 

 in search of more food, the caterpillar one clay 

 found itself compelled by an inner monitor 

 to alter its habits. Why, it knew not ; but, 

 just as a tired child sinks to sleep, the gorged 

 and full-fed caterpillar sank peacefully into a 

 dormant state. Then its tissues melted one by 

 one into a kind of organic pap, and its outer 

 skin hardened into a chrysalis. Within that 

 solid case new limbs and organs began to 

 grow by hereditary impulses. At the same 

 time the form of the nervous system altered, 



L 2 



